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Line 58: − − + − [[file:sem-xrd-cl-and-xf-methods_fig1.png|thumb|left|{{figure number|1}}Schematic drawing of a common scanning electron microscope showing how the sample is “iluminated” by an electron beam and amplified for viewing by the operator.]]+ + + + + + + − − [[file:sem-xrd-cl-and-xf-methods_fig2.png|thumb|{{figure number|2}}X-ray diffraction configuration. Knowledge of the wavelength (X) and angle of incidence allows the ''d'' spacing to be calculated.]] − − [[file:sem-xrd-cl-and-xf-methods_fig3.png|left|thumb|{{figure number|3}}X-ray diffraction patterns.]] − − [[file:sem-xrd-cl-and-xf-methods_fig4.png|thumb|{{figure number|4}}Schematic drawing showing how a typical cathodoluminescence system works. Depending on the manufacturer, the location of the cathode tube may differ.]] − − [[file:sem-xrd-cl-and-xf-methods_fig5.png|thumb|left|{{figure number|5}}A photomicrograph taken under cathodoluminescence showing concentric zoning in dolomite cement. High Mn<sup>+2</sup> dolomite shows up as bright bands and higher Fe<sup>+2</sup> dolomite as dark bands. Copyright: W. J. Myers.]] Line 96:
Line 93: − − [[file:sem-xrd-cl-and-xf-methods_fig6.png|thumb|{{figure number|6}}(a) X-ray fluoroscopy slab photograph and (b) plane light slab photograph of a Pennsylvanian sandstone from Oklahoma.]]
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| Image often defines hidden character of sample, e.g., may show directional [[porosity]] and flow boundaries, internal structures of fossils.
| Image often defines hidden character of sample, e.g., may show directional [[porosity]] and flow boundaries, internal structures of fossils.
| * Voltage increase decreases contrast in image. * Shielding required. * Carbonate photos often lack detail because mineral variety simpler than siliciclastics. * Samples must be relatively thin.
| * Voltage increase decreases contrast in image. * Shielding required. * Carbonate photos often lack detail because mineral variety simpler than siliciclastics. * Samples must be relatively thin.
|}
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==Scanning electron microscopy (SEM)==
==Scanning electron microscopy (SEM)==
<gallery>
file:sem-xrd-cl-and-xf-methods_fig1.png|{{figure number|1}}Schematic drawing of a common scanning electron microscope showing how the sample is “iluminated” by an electron beam and amplified for viewing by the operator.
file:sem-xrd-cl-and-xf-methods_fig2.png|{{figure number|2}}X-ray diffraction configuration. Knowledge of the wavelength (X) and angle of incidence allows the ''d'' spacing to be calculated.
file:sem-xrd-cl-and-xf-methods_fig3.png|{{figure number|3}}X-ray diffraction patterns.
file:sem-xrd-cl-and-xf-methods_fig4.png|{{figure number|4}}Schematic drawing showing how a typical cathodoluminescence system works. Depending on the manufacturer, the location of the cathode tube may differ.]]
file:sem-xrd-cl-and-xf-methods_fig5.png|{{figure number|5}}A photomicrograph taken under cathodoluminescence showing concentric zoning in dolomite cement. High Mn<sup>+2</sup> dolomite shows up as bright bands and higher Fe<sup>+2</sup> dolomite as dark bands. Copyright: W. J. Myers.
file:sem-xrd-cl-and-xf-methods_fig6.png|{{figure number|6}}(a) X-ray fluoroscopy slab photograph and (b) plane light slab photograph of a Pennsylvanian sandstone from Oklahoma.
</gallery>
In SEM analysis, samples up to [[length::4 in.]] in diameter are struck by a focused beam of electrons in a vacuum chamber ([[:file:sem-xrd-cl-and-xf-methods_fig1.png|Figure 1]]). The secondary and reflected primary electrons are detected and amplified. However, the sample must be conductive to the beam and generally is coated with a very thin layer of carbon or gold-palladium. A spectrum of X-rays are generated as the beam hits the sample. The X-radiation is resolved into characteristic peaks for various elements from fluorine (atomic number 2 = 9) and up. The images are recorded by photograph or video.
In SEM analysis, samples up to [[length::4 in.]] in diameter are struck by a focused beam of electrons in a vacuum chamber ([[:file:sem-xrd-cl-and-xf-methods_fig1.png|Figure 1]]). The secondary and reflected primary electrons are detected and amplified. However, the sample must be conductive to the beam and generally is coated with a very thin layer of carbon or gold-palladium. A spectrum of X-rays are generated as the beam hits the sample. The X-radiation is resolved into characteristic peaks for various elements from fluorine (atomic number 2 = 9) and up. The images are recorded by photograph or video.
From the recorded three-dimensional images, the morphology of mineral and nonmineral grains and matrix samples can be documented. Pore roughness and interconnectedness can be evaluated. These data can then be related to reservoir flow parameters such as [[permeability]] and log response.<ref name=pt05r127>Pittman, E. D., 1979, [[Porosity]], diagenesis, and productive capability of sandstone reservoirs, in Scholle, P. A., Schluger, P. R., eds., Aspects of Diagenesis: Society Economic Paleontologists and Mineralogists Special Publication 26, p. 159–173.</ref> (For information on how grain and pore morphology affect permeability, see [[Permeability]].)
From the recorded three-dimensional images, the morphology of mineral and nonmineral grains and matrix samples can be documented. Pore roughness and interconnectedness can be evaluated. These data can then be related to reservoir flow parameters such as [[permeability]] and log response.<ref name=pt05r127>Pittman, E. D., 1979, [[Porosity]], diagenesis, and productive capability of sandstone reservoirs, in Scholle, P. A., Schluger, P. R., eds., Aspects of Diagenesis: Society Economic Paleontologists and Mineralogists Special Publication 26, p. 159–173.</ref> (For information on how grain and pore morphology affect permeability, see [[Permeability]].)
==X-ray diffraction (XRD)==
==X-ray diffraction (XRD)==
The principal advantage of XRD is that a qualitative or semiquantitative evaluation of mineralogy is generated. A fixed wavelength X-ray source such as copper X-ray tubes, which have a 1.54A wavelength, is used to irradiate a powdered sample. The incident angle 9 (theta) of the diffracted beam and the intensity are recorded with a counter or tube ([[:file:sem-xrd-cl-and-xf-methods_fig2.png|Figure 2]]). If parallel planes of atoms of a crystal are struck at the same angle, coherent (additive) intensity is detected and recorded as a peak. Bragg's Law (see <ref name=pt05r43>Cullity, B. D., 1959, Elements of X-ray Diffraction: Reading, MA, Addison-Wesley, 514 p.</ref>) is the basis for determining the characteristic peaks (''d'' spacing) for known minerals and compounds (''n''λ = 2''d'' sin θ). Tables of standards established by the JCPDS (Joint Council of Powder Diffraction Standards) can be consulted for mineral identification, where 6 is the incident angle, λ the X-ray wavelength and ''d'' the spacing between planes of atoms in the crystal.
The principal advantage of XRD is that a qualitative or semiquantitative evaluation of mineralogy is generated. A fixed wavelength X-ray source such as copper X-ray tubes, which have a 1.54A wavelength, is used to irradiate a powdered sample. The incident angle 9 (theta) of the diffracted beam and the intensity are recorded with a counter or tube ([[:file:sem-xrd-cl-and-xf-methods_fig2.png|Figure 2]]). If parallel planes of atoms of a crystal are struck at the same angle, coherent (additive) intensity is detected and recorded as a peak. Bragg's Law (see <ref name=pt05r43>Cullity, B. D., 1959, Elements of X-ray Diffraction: Reading, MA, Addison-Wesley, 514 p.</ref>) is the basis for determining the characteristic peaks (''d'' spacing) for known minerals and compounds (''n''λ = 2''d'' sin θ). Tables of standards established by the JCPDS (Joint Council of Powder Diffraction Standards) can be consulted for mineral identification, where 6 is the incident angle, λ the X-ray wavelength and ''d'' the spacing between planes of atoms in the crystal.
Nonminerals such as solid hydrocarbons or glass cannot be identified by XRD because they lack sufficient internal structure.
Nonminerals such as solid hydrocarbons or glass cannot be identified by XRD because they lack sufficient internal structure.
Determination of bulk rock mineralogy is obtained from combined diffraction analysis of bulk powder and oriented mounts. Powder mounts are best for identification of nonplaty minerals. Platy minerals are best analyzed in slurries dried on metal, glass, or ceramic holders. This is especially true for clays with particle sizes ≤5 μm. Abundances are then determined by measuring peak intensity or half area for the diffraction peaks of the major three to five diffraction peaks of each mineral ([[:file:sem-xrd-cl-and-xf-methods_fig3.png|Figure 3]]). A limitation of this method is the inability to determine abundances of mineral species (such as quartz from chert) or polymineral grains (such as granite from separate feldspar and quartz).
Determination of bulk rock mineralogy is obtained from combined diffraction analysis of bulk powder and oriented mounts. Powder mounts are best for identification of nonplaty minerals. Platy minerals are best analyzed in slurries dried on metal, glass, or ceramic holders. This is especially true for clays with particle sizes ≤5 μm. Abundances are then determined by measuring peak intensity or half area for the diffraction peaks of the major three to five diffraction peaks of each mineral ([[:file:sem-xrd-cl-and-xf-methods_fig3.png|Figure 3]]). A limitation of this method is the inability to determine abundances of mineral species (such as quartz from chert) or polymineral grains (such as granite from separate feldspar and quartz).
==Cathodoluminescence (CL)==
==Cathodoluminescence (CL)==
In CL, electrons from a cold cathode discharge tube strike a rock surface in a vacuum chamber ([[:file:sem-xrd-cl-and-xf-methods_fig4.png|Figure 4]]). In a strong vacuum, energy imparted to electrons in activator ions within the grain causes luminescence. The principle activator ions are manganese and lead.<ref name=pt05r107>Machel, H-G., 1985, Cathodoluminescence in calcite and dolomite and its chemical interpretation: Geoscience Canada, v. 12, p. 139–147.</ref> Concentrations need be in the 100 ppm range to affect the grain. Other rare earth elements such as dysprosium are also activators. Ferric iron (+3) is the most common quenching ion. The emitted color, when observed, shows the zonations in activator ion concentrations related to the type of crystallization or thermal histories of the host minerals ([[:file:sem-xrd-cl-and-xf-methods_fig5.png|Figure 5]]). Lattice defect structures in quartz are also thought to cause some CL in quartz.
In CL, electrons from a cold cathode discharge tube strike a rock surface in a vacuum chamber ([[:file:sem-xrd-cl-and-xf-methods_fig4.png|Figure 4]]). In a strong vacuum, energy imparted to electrons in activator ions within the grain causes luminescence. The principle activator ions are manganese and lead.<ref name=pt05r107>Machel, H-G., 1985, Cathodoluminescence in calcite and dolomite and its chemical interpretation: Geoscience Canada, v. 12, p. 139–147.</ref> Concentrations need be in the 100 ppm range to affect the grain. Other rare earth elements such as dysprosium are also activators. Ferric iron (+3) is the most common quenching ion. The emitted color, when observed, shows the zonations in activator ion concentrations related to the type of crystallization or thermal histories of the host minerals ([[:file:sem-xrd-cl-and-xf-methods_fig5.png|Figure 5]]). Lattice defect structures in quartz are also thought to cause some CL in quartz.
There has been much discussion on fluoroscopy applications using fluorescent dyes at low magnification related to coals and other minerals. [[:file:sem-xrd-cl-and-xf-methods_fig6.png|Figure 6]] shows the difference between irradiated and normal incident light for a sample. Note the short vertical fractures accentuated in the fluoroscopy photograph.
There has been much discussion on fluoroscopy applications using fluorescent dyes at low magnification related to coals and other minerals. [[:file:sem-xrd-cl-and-xf-methods_fig6.png|Figure 6]] shows the difference between irradiated and normal incident light for a sample. Note the short vertical fractures accentuated in the fluoroscopy photograph.
==See also==
==See also==